Method of producing optical recording medium by transfer process using a stamper, and optical recording medium produced thereby

ABSTRACT

A method for producing an optical recording medium of the present invention including a first laminating step, a second transferring step, a third detaching step, and a fourth forming step. The first step includes laminating a substrate and a transfer stamper with an uncured ultraviolet-curable resin interposed therebetween. The transfer stamper has recesses/projections that provide information to be transferred. The second step includes transferring the information to be transferred of the transfer stamper onto a surface of the ultraviolet-curable resin. The third step includes detaching the transfer stamper from the ultraviolet-curable resin at an interface therebetween after the ultraviolet-curable resin is cured. The fourth step includes forming a thin film layer on the information-transferred surface of the ultraviolet-curable resin. The thin film layer includes either a recording film or a reflection film. The method requires that either a weight of the transfer stamper or a viscosity of the ultraviolet-curable resin is set so that a surface roughness of the information-transferred surface of the ultraviolet-curable resin is smaller than a surface roughness of the surface of the transfer stamper on which the information to be transferred is provided.

TECHNICAL FIELD

The present invention relates to an optical recording medium forreproduction or for recording and reproduction, and to a method forproducing the same.

BACKGROUND ART

Recently, with an increase in the information amount that informationdevices and audiovisual devices are required to process, optical disksthat are superior in allowing for easy data access, large capacity datastorage, and reduction of device sizes have attracted more attention asrecording media, and the recording of information at a higher densityhas been attempted. For instance, as an optical disk with a higherdensity, an optical disk having a capacity of approximately 25 GB hasbeen proposed to which the recording and reproduction is performed withthe use of a recording/reproduction head whose recording/reproductionlaser beam source emits light with a wavelength of approximately 400 nmand whose objective lens for converging a laser beam has a numericalaperture (NA) of 0.85.

The following will describe a configuration of a conventional opticaldisk and a method for producing the same, while referring to FIGS. 2 to5. FIGS. 2A to 2F illustrate a method for producing a nickel (Ni)stamper as a substrate mold for use in the production of a conventionaloptical disk. In the production of the Ni stamper, first of all, aphotosensitive film 202 is formed on a glass plate 201 by applying aphotosensitive material such as a photoresist thereon (see FIG. 2A), andrecording track portions are exposed by optical recording with use of alaser beam 203 (see FIG. 2B). In FIG. 2B, 202 a denotes an exposedportion. The photosensitive material in the recording track portionsthus exposed is removed through a developing process, and an opticalrecording master 205 in which a recording track pattern 204 is formed isproduced (see FIG. 2C). The pattern of the recording track pattern 204formed on the photosensitive film 202 is transferred to a conductivefilm 206 (material: Ni) formed by sputtering or vapor deposition (seeFIG. 2D). Furthermore, to increase the rigidity and thickness of theconductive film 206, a Ni plating film 207 is formed (see FIG. 2E).Then, the conductive film 206 and the Ni plating film 207 are detachedat an interface between the photosensitive film 202 and the conductivefilm 206, so that a Ni stamper 208 is produced (see FIG. 2F).

FIG. 3 illustrates a cross section of a thick-substrate transfer-typeoptical disk as a conventional optical disk. The thick-substratetransfer-type optical disk includes a first substrate 302 having asurface on one side on which recesses/projections are provided as signalpits or recording tracks, a thin film layer 301 provided on the surfaceof the first substrate 302 on which the recesses/projections areprovided, a second substrate 303 arranged facing the first substrate302, and a transparent layer 304 interposed between the first substrate302 and the second substrate 303 so as to cause them to adhere with eachother.

Signal pits or recording tracks are transferred in a form of recessesonto one side of the first substrate 302 by injection compressionmolding or the like using the Ni stamper 208 shown in FIG. 2F. The firstsubstrate 302 has a thickness of approximately 1.1 mm. The thin filmlayer 301 includes a recording film and/or a reflection film, and isformed by sputtering, vapor deposition, or the like on the surface ofthe first substrate 302 on which signal pits or recording tracks areformed. The second substrate 303 is made of a material that istransparent (has transparency) with respect to recording/reproductionlight, and has a thickness of approximately 0.1 mm. The transparentlayer 304 is provided to cause the two substrates 302 and 303 to adherewith each other, and is made of an adhesive such as ultraviolet-curableresin or the like.

The recording/reproduction of such a conventional thick-substratetransfer-type optical disk is carried out by projecting arecording/reproduction laser beam thereto from the second substrate 303side.

Furthermore, FIG. 4 illustrates a cross section of a thin-substratetransfer-type optical disk as another conventional optical disk. Thethin-substrate transfer-type optical disk includes a first substrate402, a signal transfer layer 405 provided on the first substrate 402that has a surface on one side on which recesses/projections areprovided as signal pits or recording tracks, a thin film layer 401provided on the surface of the signal transfer layer 405 on which therecesses/projections are provided, a second substrate 403 arrangedfacing the first substrate 402, and a transparent layer 404 interposedbetween the first substrate 402 and the second substrate 403 so as tocause them to adhere with each other.

The first substrate 402 is made of a material that is transparent (hastransparency) with respect to recording/reproduction light, and has athickness of approximately 0.1 mm. The signal transfer layer 405 is alayer made of an ultraviolet-curable resin, on one of whose surfacesrecesses are formed by compression transfer using the Ni stamper 208shown in FIG. 2F so as to provide signal pits or recording tracks. Thecompression transfer with the ultraviolet-curable resin is performed bydripping the ultraviolet-curable resin concentrically on the firstsubstrate 402, applying the Ni stamper 208 thereon so that aninformation surface (surface where the recording pattern 204 isprovided) of the Ni stamper 208 faces the first substrate 402, andapplying a pressure on the transfer stamper 208. Thus, the spreading ofthe ultraviolet-curable resin and the transfer of the pattern of theinformation surface are performed. The thin film layer 401 includes arecording film and/or a reflection film, which are formed by sputteringor vapor deposition on the surface of the signal transfer layer 405 onwhich signal pits or recording tracks are formed. The second substrate403 has a thickness of approximately 1.1 mm. The transparent layer 404is provided to cause the two substrates 402 and 403 to adhere with eachother, and is made of an adhesive such as ultraviolet-curable resin orthe like.

The recording/reproduction of such a conventional thin-substratetransfer-type optical disk is carried out by projecting arecording/reproduction laser beam thereto from the first substrate 402side.

The following will describe a configuration of an optical disk in whicha phase-change recording material is used for forming the thin filmlayer so as to form a recording film, so that the optical disk ismodified to be a phase-change optical disk. FIG. 5 is an enlargedcross-sectional view illustrating a configuration of the thick-substratetransfer-type optical disk shown in FIG. 3 in which a phase-changerecording material is used for forming the thin film layer 301 so as toform a recording film. In the thick-substrate transfer-type opticaldisk, recording tracks are formed on an information surface 302 a of thefirst substrate 302 as the thick substrate. The recording tracks aregrooves formed with recesses/projections at a track pitch 505 ofapproximately 0.3 μm. Furthermore, a reflection film 501 made of AgPdCuor the like, a dielectric film 502 made of a dielectric material such asZnS—SiO₂, a recording film 503, and a dielectric film 504 made of adielectric material such as ZnS—SiO₂ are formed by sputtering or thelike. The recording film 503 is formed by sputtering or the like, with amaterial such as Ge (germanium), Sb (antimony), and Te (tellurium). Thedielectric films 502 and 504 are provided so as to protect the recordingfilm 503 from damage caused by heat, moisture, etc. These reflectionfilm 501, the dielectric films 502 and 504, and the recording film 503compose the thin film layer 301.

A phase-change recording material makes a transition into an amorphousstate in the case where it is cooled abruptly after it is molten,whereas it makes a transition into a crystalline state in the case whereit is cooled gradually after it is heated. An optical disk having arecording film that is made of such a phase-change recording material bytaking advantage of the foregoing property makes reversible transitionsbetween the crystalline state and the amorphous state, thereby beingcapable of overwriting. The reproduction of signals on the optical diskis performed in the following manner: while focusing control andtracking control are carried out so that a reproduction laser beamhaving a small constant intensity is positioned on a groove track inwhich signals are recorded, a change in an amount of light reflectedfrom the optical disk is detected by a photodetector device, utilizing aproperty such that amorphous portions as recording marks and crystallineportions other than the recording marks have different reactances ordifferent transmittances. It should be noted that FIG. 5 illustrates anexample of the thick-substrate transfer-type optical disk shown in FIG.3 modified by using a phase-change recording material to form the thinfilm layer 301, and in the case of the thin-substrate transfer-typeoptical disk shown in FIG. 4, it also is possible to form the thin filmlayer 401 using a phase-change recording material.

A phase-change optical disk in which the thin film layer 301 or 401 isformed with a phase-change recording material is described as theforegoing conventional optical disk, but it is possible to provide anoptical disk that is capable of reproduction solely by forming signalpits on the substrate and forming a reflection film in the thin filmlayer 301 or 401.

However, with an increase in the density of an optical recording medium,the reproduction of an optical recording medium is affected by finerecesses/projections on the optical recording medium as noise sourcesmore than before. In the case where, like a Ni stamper used in theproduction of a conventional optical disk, a Ni stamper is producedthrough the laser exposure of a photosensitive material such as aphotoresist for recording signal pits or recording tracks, which isfollowed by the development, the sputtering and the plating, theroughness of the photosensitive material and the like due to thecoarseness of the photosensitive material or caused by a developer istransferred to the Ni stamper from the photosensitive material surface,thereby leaving fine recesses/projections on the Ni stamper. Therefore,in the case where an optical disk is produced using such a Ni stamper,the fine recesses/projections become noise sources. In the case wherethe injection compression molding or the compression transfer of anultraviolet-curable resin is used for transferring a surface state of atransfer stamper to a substrate, the surface roughness of the stamper istransferred to the substrate in detail by compression. Therefore, anoptical disk including such a substrate has high reproduction noise.Furthermore, in the foregoing production by the injection compressionmolding or compression transfer with use of an ultraviolet-curable resinin which the foregoing Ni stamper is employed, it is difficult to form,on a substrate surface, signal pits or recording tracks withrecesses/projections that have a uniform depth/height (level differencebetween bottoms of the recesses and tops of the projections) therebyproviding high reproducibility, or alternatively, to make uniform withina disk surface a sum of thicknesses of a thin substrate and anultraviolet-curable resin that determines the conversion of arecording/reproduction laser light upon the recording/reproduction of asignal surface of a thin-substrate transfer-type optical disk.

DISCLOSURE OF THE INVENTION

Therefore, a method for producing an optical recording medium accordingto the present invention includes: a first step of laminating asubstrate and a transfer stamper with a not cured ultraviolet-curableresin interposed therebetween, the transfer stamper having, on at leastone of the surfaces thereof, recesses/projections that provideinformation to be transferred; a second step of transferring theinformation to be transferred of the transfer stamper onto a surface ofthe ultraviolet-curable resin; a third step of detaching the transferstamper from the ultraviolet-curable resin at an interface therebetweenafter the ultraviolet-curable resin is cured; and a fourth step offorming a thin film layer on the information-transferred surface of theultraviolet-curable resin, the thin film layer including at least one ofa recording film and a reflection film. In the method, at least one of aweight of the transfer stamper and a viscosity of theultraviolet-curable resin is set so that a surface roughness of theinformation-transferred surface of the ultraviolet-curable resin issmaller than a surface roughness of the surface of the transfer stamperon which the information to be transferred is provided.

Furthermore, an optical recording medium of the present invention isproduced by the foregoing optical recording medium producing method ofthe present invention described above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an optical disk according toEmbodiment 1, which is produced by an optical recoding medium producingmethod of the present invention.

FIGS. 2A to 2F are cross-sectional views illustrating a process ofproducing a stamper for use in an optical disk substrate production.

FIG. 3 is a cross-sectional view illustrating a thick-substratetransfer-type optical disk as an example of an optical disk produced bya conventional optical recording medium producing method.

FIG. 4 is a cross-sectional view illustrating a thin-substratetransfer-type optical disk as an example of an optical disk produced bya conventional optical recording medium producing method.

FIG. 5 is an enlarged cross-sectional view illustrating a thin filmlayer of a thick-substrate transfer-type optical disk as an example ofan optical disk produced by a conventional optical recording mediumproducing method.

FIGS. 6A to 6E are cross-sectional views illustrating an example of aprocess of an optical recording medium producing method of the presentinvention.

FIG. 7 is an enlarged cross-sectional view illustrating a thin filmlayer of an optical disk produced by an optical recording mediumproducing method of the present invention.

FIG. 8A is a cross-sectional view illustrating a state of reproductionof a thick-substrate transfer-type optical disk as an example of anoptical disk produced by a conventional optical recording mediumproducing method, and FIG. 8B is a cross-sectional view illustrating astate of reproduction of an optical disk produced by the opticalrecording medium producing method of the present invention.

FIG. 9 is a cross-sectional view of an optical disk according toEmbodiment 2 produced by an optical recording medium producing method ofthe present invention.

FIGS. 10A to 10E are cross-sectional views illustrating another exampleof a production process of an optical recording medium producing methodof the present invention.

DESCRIPTION OF THE INVENTION

A method for producing an optical recording medium according to thepresent invention includes: a first step of laminating a substrate and atransfer stamper with a not cured ultraviolet-curable resin interposedtherebetween, the transfer stamper having, on at least one of surfacesthereof, recesses/projections that provide information to betransferred; a second step of transferring the information to betransferred of the transfer stamper onto a surface of theultraviolet-curable resin; a third step of detaching the transferstamper from the ultraviolet-curable resin at an interface therebetweenafter the ultraviolet-curable resin is cured; and a fourth step offorming a thin film layer on the information-transferred surface of theultraviolet-curable resin, the thin film layer including at least one ofa recording film and a reflection film. In the method, at least one of aweight of the transfer stamper and a viscosity of theultraviolet-curable resin is set so that a surface roughness of theinformation-transferred surface of the ultraviolet-curable resin issmaller than a surface roughness of the surface of the transfer stamperon which the information to be transferred is provided. This methodmakes it possible to prevent fine recesses/projections present on thesurface of the transfer stamper on which information to be transferredis provided from being transferred onto the surface of theultraviolet-curable resin that constitutes an information surface of theoptical recording medium. By so doing, it is possible to provide anoptical recording medium with reduced reproduction noises.

In the foregoing optical recording medium producing method of thepresent invention, in the second step, spinning preferably is carriedout in a state in which the substrate and the transfer stamper arelaminated so that the ultraviolet-curable resin is spread and theinformation to be transferred from the transfer stamper is transferredto the ultraviolet-curable resin. This is intended to allow theultraviolet-curable resin to be formed with a uniform thickness insidethe surface, and further, to allow information that is expressed as, forinstance, a pattern of recesses/projections forming signal pits orrecording tracks to be transferred with excellent uniformity andreproducibility onto the ultraviolet-curable resin.

In the optical recording medium producing method of the presentinvention, the ultraviolet-curable resin preferably has a viscosity ofnot less than 30 mPa·s and not more than 4000 mPa·s, more preferably,not less than 30 mPa·s and not more than 500 mPa·s. This causes theinformation to be transferred of the transfer stamper to be transferredto the ultraviolet-curable resin with a smaller depth, so as to preventthe surface roughness of the transfer stamper from being transferred tothe ultraviolet-curable resin. It should be noted that this viscosity isa value measured in an environmental condition of 20° C. to 25° C.

In the optical recording medium producing method of the presentinvention, a depth/height of recesses/projections formed on theultraviolet-curable resin as a result of the transfer preferably is 5%to 30% smaller, more preferably, 5% to 20% smaller, than thedepth/height of the recesses/projections of the transfer stamper thatprovide information to be transferred. This is intended to prevent thesurface roughness of the transfer stamper from being transferred to theultraviolet-curable resin.

In the optical recording medium producing method of the presentinvention, a track pitch of recording tracks or signal pits to betransferred that are included in the information to be transferred ofthe transfer stamper preferably is 0.25 μm to 0.8 μm. The reason is asfollows. A track pitch of greater than 0.80 μm causes the surfaceroughness of the transfer stamper to be transferred onto theultraviolet-curable resin in detail, thereby increasing the reproductionnoise. Furthermore, a track pitch of smaller than 0.25 μm makes itdifficult to perform uniform transfer within the surface, therebycausing transfer irregularities.

In the optical recording medium producing method of the presentinvention, a width of the recording tracks to be transferred or a widthof the signal pits preferably is 30% to 70% of the track pitch. This isintended to obtain excellent signal characteristics or tracking controlsignal characteristics upon recording/reproduction.

In the optical recording medium producing method of the presentinvention, a depth of recording tracks or signal pits to be transferredthat are included in the information to be transferred of the transferstamper preferably is 10 nm to 100 nm.

In the optical recording medium producing method of the presentinvention, the transfer stamper preferably has a weight per unit area of0.03 g/cm² to 0.20 g/cm². This is intended to allow the information tobe transferred of the transfer stamper to be transferred onto theultraviolet-curable resin with a smaller depth, so as to prevent thesurface roughness of the transfer stamper from being transferred ontothe ultraviolet-curable resin.

In the optical recording medium producing method of the presentinvention, the transfer stamper preferably is made of a resin material.This allows information such as recording tracks or signal pits to beformed easily, and enables the subtle control of weight.

In the optical recording medium producing method of the presentinvention, the recording film can be made of a phase-change recordingfilm material. This is intended to form an overwritable phase-changerecording medium.

In the optical recording medium producing method of the presentinvention, the thin film layer can be composed of only a reflectionfilm. This is intended to reproduce signals of the optical recordingmedium with reflected light.

In the optical recording medium producing method of the presentinvention, the stamper preferably is positioned on an upper side withrespect to the substrate. This is intended to utilize the weight of thetransfer stamper itself in spreading the ultraviolet-curable resin andperforming the transfer to the ultraviolet-curable resin.

In the optical recording medium producing method of the presentinvention, the transfer stamper preferably has a thickness of 0.3 mm to1.1 mm. The reason is as follows. In the case where the transfer stamperhas a thickness of less than 0.3 mm, the rigidity thereof decreases,thereby allowing warpage to occur easily. On the other hand, a thicknessthereof of more than 1.1 mm makes it difficult to perform spinning in astate in which the transfer stamper and the first substrate arelaminated.

An optical recording medium of the present invention is produced by theoptical recording medium producing method of the present inventiondescribed above. With this, an optical recording medium with reducedproduction noise can be provided.

The following will describe embodiments of the present invention whilereferring to the drawings.

EMBODIMENT 1

FIG. 1 is a cross-sectional view illustrating an optical disk accordingto an embodiment of an optical recording medium of the presentinvention. An optical disk according to the present embodiment includesa first substrate 101 as a thick substrate, a signal transfer layer 102,a thin film layer 103, a second substrate 105, and a transparent layer104. The signal transfer layer 102 is provided on a surface of the firstsubstrate 101 and has a pattern of recesses/projections of signal pits,recording tracks, etc. on a surface on a side opposite to the firstsubstrate 101. The thin film layer 103 is provided on the surface of thesignal transfer layer 102 having the pattern of recesses/projections.The second substrate 105 is a thin substrate arranged facing the firstsubstrate 101. The transparent layer 104 is provided so as to cause thefirst substrate 101 and the second substrate 105 to adhere to eachother.

To form the first substrate 101, an approximately 1.1 mm-thick disk madeof polycarbonate is used so as to prevent warpage and improve therigidity of a resulting disk and to provide a thickness compatibilitythereof with an optical disk such as a CD or a DVD. The signal transferlayer 102 is made of an ultraviolet-curable resin, and has projectionson one side to form signal pits or recording tracks, which are formed bytransferring a pattern of a transfer stamper. The transfer stamper isformed by applying a resin such as polycarbonate onto a conventional Nistamper shown in FIG. 2F by injection compression molding or the like,and has a pattern of recesses/projections on at least one side thereofas information to be transferred. To form the transfer stamper, a diskis used in which recording tracks or signal pits are formed withrecesses so that a track pitch is approximately 0.25 μm to 0.8 μm andeach groove has a width of approximately 30% to 70% of the track pitch,with a view to obtaining excellent signal characteristics or excellenttracking control signal characteristics upon recording/reproduction.

FIGS. 6A to 6E illustrate a process through which the signal transferlayer 102 is formed on the first substrate 101 as a base. First of all,a first substrate 601 as a base is fixed on a turntable 602 by a diskcentering jig 603 provided substantially at the center of the turntable602 as well as by suction of a plurality of small vacuum holes (notshown) provided on an upper surface of the turntable 602, so as toreduce the eccentricity of the first substrate 601 from a rotationalaxis of the turntable 602 when the first substrate 601 is placed on theturntable 602 (see FIG. 6A). An ultraviolet-curable resin 604 is appliedwith a dispenser on the first substrate 601 fixed on the turntable 602so that the ultraviolet-curable resin 604 is spread over a range of apredetermined radius substantially in a concentric form (see FIG. 6B).Furthermore, a transfer stamper 605 is laminated on the first substrate601 on which the ultraviolet-curable resin 604 is applied so that aninformation surface of the transfer stamper 605 faces the firstsubstrate 601.

The ultraviolet-curable resin 604 is spread by spinning the turntable602 in a state in which the first substrate 601 and the transfer stamper605 are laminated (see FIG. 6C), while simultaneously a pattern ofrecesses/projections forming the recording tracks or signal pits on theinformation surface of the transfer stamper 605 are transferred onto asurface of the ultraviolet-curable resin 604. Here, theultraviolet-curable resin 604 flows toward a periphery due to acentrifugal force generated by the spinning, which tends to make itdifficult to fill the ultraviolet-curable resin 604 in a central portioninside the range of the predetermined radius to which theultraviolet-curable resin 604 is dripped. To compensate this, theultraviolet-curable resin 604 between the first substrate 601 and thetransfer stamper 605 may be sucked toward the central portion by avacuum drawing mechanism 6A provided at the centering jig 603.Furthermore, in order to transfer the pattern formed on the informationsurface of the transfer stamper 605 to the ultraviolet-curable resin 604at a rate of approximately 90% of a depth/height therecesses/projections (in order to transfer the pattern so thatrecesses/projections formed on the ultraviolet-curable resin 604 bytransfer have a depth/height approximately 10% smaller than thedepth/height of the recesses/projections formed on the informationsurface of the transfer stamper 605 as information to be transferred), aresin containing, for instance, an acrylic resin as a principalcomponent, having a viscosity of approximately 150 mPa·s in the useenvironment (ambient temperature is 20° C. To 25° C., which applies tothe viscosities described below), is used as the ultraviolet-curableresin 604, while a disk made of polycarbonate that is 120 mm in diameterand 1.1 mm in thickness, has a center hole at center with a diameter of30 mm, and is approximately 16 g in weight (weight per unit area: 0.15g/cm²) is used as the transfer stamper 605. It should be noted that,other than polycarbonate, a polyolefin-based resin or an acryl-basedresin may be used for forming the transfer stamper 605.

Since the transfer stamper 605 is made of a resin, it is possible toform recording tracks or signal pits easily, and since it has a smallmass, the variation of thickness thereof ensures subtle control of theweight of the transfer stamper. Furthermore, in the case where a stampermade of Ni or another material is used as in the prior art, the transfercontrol is difficult since the material has an inferior detachabilityfrom an ultraviolet-curable resin used for forming the signal transferlayer. In contrast, however, in the case where the stamper is made of aresin as in the present invention, the foregoing problem can be solvedby selecting a resin having a superior detachability from anultraviolet-curable resin used for forming the signal transfer layer.Moreover, since the ultraviolet-curable resin is spread by spinning, itis possible to make the transfer within the disk surface and thethickness of the ultraviolet-curable resin uniform. In other words,since the weight of the transfer stamper itself is utilized forachieving the transfer without the application of pressure to thetransfer stamper as in the prior art, irregular flow of the resin causedby the mechanical application of pressure by no means occurs.

The ultraviolet-curable resin 604 formed between the first substrate 601and the transfer stamper 605 is cured when ultraviolet light is appliedthereto by an ultraviolet projector 606 (see FIG. 6D), and thereafter,the transfer stamper 605 is detached from the ultraviolet-curable resin604 at an interface therebetween. Thus, on the first substrate 601(corresponding to the first substrate 101 in FIG. 1), anultraviolet-curable resin layer is formed on which the pattern ofrecesses/projections of the transfer stamper 605 is transferred with adepth/height of approximately 90% of the depth/height of therecesses/projections on the transfer stamper 605: namely, a signaltransfer layer 607 (corresponding to the signal transfer layer 102 inFIG. 1) is formed (see FIG. 6E).

As a means for detachment, for instance, a region 6B in which theultraviolet-curable resin 604 is not filled may be secured in thecentral portion in a disk obtained by combining the first substrate 601and the transfer stamper 605 with each other, and a mechanical detachingjig may be inserted or compressed air may be injected between the firstsubstrate 601 and the transfer stamper 605. By so doing, they aredetached uniformly in a radial direction of the disk. In the case wherethe material of the transfer stamper 605 is selected with thedetachability thereof taken into consideration so as to ensure thedetachment at an interface between the ultraviolet-curable resin 604 andthe transfer stamper 605, a polyolefin-based resin preferably isselected. Here, a surface roughness of space tracks on the transferstamper 605 was determined to be 3 nm according to the measurement by anatomic force microscope, whereas a surface roughness of space tracksformed on the signal transfer layer 607 corresponding to the foregoingtransfer stamper 605 was determined to be 1 nm. After the signaltransfer layer 607 is formed, a thin film layer 103 including aphase-change recording film capable of repetitive recording/reproductionis formed on the signal transfer layer 607 by sputtering or the likeprincipally.

The transparent layer 104 formed when the thin film layer 103 and thesecond substrate 105 as the thin substrate are caused to adhere to eachother is made of an ultraviolet-curable resin substantially transparentwith respect to recording/reproduction light (having transparency),containing, for instance, an acrylic resin as a principal component. Thetransparent layer 104 is formed in the following manner. First of all,an ultraviolet-curable resin is applied over at least one of the thinfilm layer 103 and the second substrate 105, and is subjected tospinning so that air bubbles contained in the ultraviolet-curable resinare removed and the thickness thereof is controlled, and thereafterultraviolet rays are projected thereto so as to cure theultraviolet-curable resin. The second substrate 105 is composed of anapproximately 0.1 mm-thick disk made of polycarbonate that issubstantially transparent (has transparency) with respect torecording/reproduction light. The thickness of the transparent layer 104is controlled so that a focus position 106 where a laser light emittedfrom the recording/reproduction head is focused falls on a positiondetermined according to a sum of the thicknesses of the second substrate105 and the transparent layer 104. Thus, with the transparent layer 104(by curing the ultraviolet-curable resin), the first substrate 101 withthe signal transfer layer 102 and the thin film layer 103 providedthereon and the second substrate 105 are caused to adhere to each other.

FIG. 7 is an enlarged view of a cross section of the thin film layer 103according to the present embodiment, and the following will describe aconfiguration of the thin film layer 103 while referring to FIG. 7. Onan information-transferred surface (a surface on which information istransferred) 102 a of the signal transfer layer 102 formed on the firstsubstrate 101, a reflection film 701 made of Al, a dielectric film 702made of ZnS—SiO₂ or the like, a recording film 703, and a dielectricfilm 704 made of ZnS—SiO₂ or the like are formed by sputtering in thestated order. These reflection films 701, dielectric film 702, recordingfilm 703 and dielectric film 704 compose the thin film layer 103according to the present embodiment. The reflection film 701 has athickness of 80 nm, and is configured to be cooled rapidly so as todiffuse heat generated upon signal recording. It should be noted thatherein Al is used for forming the reflection film 701, but Ag or Au maybe used instead. Furthermore, the recording film 702 is a phase-changerecording film made of a material such as Ge, Sb, or Te, which is formedby sputtering or the like.

A conventional thick-substrate transfer-type optical disk and an opticaldisk according to the present embodiment were subjected to reproducingoperations using a recording/reproduction head with a laser wavelengthof approximately 400 nm and a numerical aperture (NA) of an objectivelens of approximately 0.85, so that noise generated upon diskreproduction were measured. Here, information on information surfaces ofthe conventional thick-substrate transfer-type optical disk and theoptical disk according to the present embodiment was reproduced byrotating the optical disks at a linear velocity of 4.5 m/s, and thelevel of disk noise at 12 MHz (in a reproduction frequency band ofsignals with a frequency of 0.375 μm) was measured by a spectrumanalyzer.

FIGS. 8A and 8B illustrate states of reproduction of the conventionalthick-substrate transfer-type optical disk shown in FIG. 3 and theoptical disk according to the present embodiment shown in FIG. 1,respectively. FIG. 8A is a view illustrating a state in which theconventional thick-substrate transfer-type optical disk is subjected toa reproducing operation, while FIG. 8B is a view illustrating a state inwhich the optical disk according to the present embodiment is subjectedto a reproducing operation. Here, a depth/height of recesses/projectionsforming recording tracks 801 on the first substrate 302 of theconventional optical disk shown in FIG. 8A was set to be 36 nm.Furthermore, in order that a depth/height of recesses/projectionsforming recording tracks 804 on the signal transfer layer 102 of theoptical disk according to the present embodiment shown in FIG. 8B shouldbe 36 nm, a depth/height of recesses/projections on the transfer stamperused for the transfer of recording tracks was set to be 40 nm.

Furthermore, to perform the measurement of the disks under the sameconditions, the recording tracks 801 of the conventional thick-substratetransfer-type optical disk that are obtained by transfer fromprojections of the Ni stamper are compared regarding disk noise with therecording tracks 804 of the optical disk according to the presentembodiment that are obtained by transfer from recesses of the resin-madetransfer stamper. Besides, space tracks 802 of the conventionalthick-substrate transfer-type optical disk that are obtained by transferfrom recesses of the Ni stamper are compared regarding disk noise withspace tracks 803 of the optical disk according to the present embodimentthat are obtained by transfer from projections of the resin-madetransfer stamper. As a result, the disk noise occurring when therecording tracks 801 of the conventional thick-substrate transfer-typeoptical disk were reproduced was −75.0 dBm at 12 MHz, while the disknoise occurring when the recording tracks 804 of the optical diskaccording to the present embodiment were reproduced was −78.2 dBm at 12MHz. Thus, the optical disk according to the present embodimentexhibited an improved property regarding disk noise of recording tracksby 3.2 dB at 12 MHz.

Furthermore, the disk noise occurring when the space tracks 802 of theconventional thick-substrate transfer-type optical disk were reproducedwas −74.0 dBm at 12 MHz, while the disk noise occurring when the spacetracks 803 of the optical disk according to the present embodiment werereproduced was −76.0 dBm at 12 MHz. Thus, the optical disk according tothe present embodiment exhibited an improved property regarding disknoise of space tracks by 2.0 dB at 12 MHz.

The reason why the improvement of the property regarding the disk noiseoccurring when the recording tracks 804 were reproduced was greater ascompared with the improvement of the property regarding the disk noiseoccurring when the space tracks 803 were reproduced is considered tostem from the difficulty in transfer of the recording tracks of thetransfer stamper to be transferred, which are the recesses of thetransfer stamper. Namely, the transfer of the recording tracks that arerecesses of the transfer stamper using a viscous ultraviolet-curableresin is difficult since the viscous ultraviolet-curable resin lesssmoothly enters the recesses. In contrast, in the transfer ofprojections of the transfer stamper corresponding to the space tracks803 to the ultraviolet-curable resin, the projections of the transferstamper are pressed against the ultraviolet-curable resin, where thepattern of the transfer stamper is transferred in more detail ascompared with the case where the ultraviolet-curable resin enters therecesses of the transfer stamper. As a result, the recording tracks 804have a surface roughness smaller than that of the space tracks 803formed by transfer, and hence, reproduction disk noise of the former issmaller than that of the latter. Besides, the reason why disk noiseoccurring upon the reproduction of the space tracks 803 to which thepattern of the transfer stamper tends to be transferred in more detailis smaller than disk noise occurring upon the reproduction of the spacetracks 802 of the thick-substrate transfer-type optical disk accordingto the prior art is that groove edges of the recording tracks 804 withan improved surface roughness condition also fall within the range ofreproduction when the space tracks 803 are reproduced.

The foregoing description refers to an example in which a pattern ofrecesses/projections that provide information to be transferred, whichis formed on the information surface of the transfer stamper 605, istransferred to the ultraviolet-curable resin 604 so thatrecesses/projections formed on the ultraviolet-curable resin 604 bytransfer have a depth/height approximately 10% smaller than thedepth/height of the recesses/projections on the information surface ofthe transfer stamper 605. However, an optical disk in which atransferred pattern has a depth/height of recesses/projections 5% to 30%smaller than the depth/height of recesses/projections of the originalpattern achieves an identical effect. It should be noted that theforegoing description mentions an example in which the transfer of thepattern of the transfer stamper is carried out using theultraviolet-curable resin 604 having a viscosity of 150 mPa·m, but ithas been confirmed that using an ultraviolet-curable resin with aviscosity in a range of 30 mPa·s to 4000 mPa·s, a pattern of recesses ofa transfer stamper was transferred to the ultraviolet-curable resin sothat a transferred pattern had a height of projections 5% to 30% smallerthan the depth of the recesses of the original pattern. Therefore, anultraviolet-curable resin 604 with a viscosity in a range of 30 mPa·s to4000 mPa·s is applicable. Furthermore, the foregoing description refersto a case where a 1.1 mm-thick disk made of polycarbonate having aweight per unit area of 0.15 g/cm² is used as the transfer stamper 605,but it has been confirmed that using a disk having a weight per unitarea in a range of 0.03 g/cm² to 0.20 g/cm², a pattern of recesses inthe transfer stamper was transferred to an ultraviolet-curable resin sothat a transferred pattern had a depth/height 5% to 30% smaller thanthat of the original pattern. Therefore, a disk having a weight per unitarea in a range of 0.03 g/cm² to 0.20 g/cm² is applicable as thetransfer stamper 605.

Therefore, a 0.6 mm-thick disk made of a resin material and having aweight per unit area of 0.08 g/cm², for instance, which is used in DVDsand the like, is applicable as a transfer stamper. It should be notedthat it is not preferable to use a disk that is made of a resin materialand has a thickness of less than 0.3 mm, since the low rigidity of thesubstrate causes warpage, which causes the thickness of theultraviolet-curable resin to be non-uniform inside the surface range,and makes it difficult to decrease a deviation between axes of the firstsubstrate and the transfer stamper. Besides, it also should be notedthat it is not desirable to use a disk that is made of a resin materialand has a thickness of more than 1.1 mm for forming the transferstamper, since the transfer stamper has an increased weight. Theincreased weight thereof makes it difficult to synchronously spin thefirst substrate and the transfer stamper that are laminated.Furthermore, such a thickness requires design change of an injectioncompression molder used in molding substrates for the conventionaloptical disks so as to change the substrate thickness set therein.

Furthermore, though the description of the present embodiment refers toas an example a case where, as shown in FIGS. 6C to 6E, theultraviolet-curable resin 604 of one type is interposed between thefirst substrate 601 and the transfer stamper 605 so as to form thesignal transfer layer 607, the ultraviolet-curable resin 604 may becomposed of two or more layers. For instance, in the case where theultraviolet-curable resin A for forming the signal transfer layer 102 isa resin having a greater adhesiveness to the transfer stamper 605 thanan adhesiveness thereof to the first substrate 601, anotherultraviolet-curable resin B may be provided between the first substrate601 and the ultraviolet resin A so as to increase the adhesivenesstherebetween. In this case, to ensure the detachment at an interfacebetween the transfer stamper 605 and the ultraviolet-curable resin A, anultraviolet-curable resin that has an adhesiveness to theultraviolet-curable resin A greater than that between theultraviolet-curable resin A and the transfer stamper 605 should beselected as the ultraviolet resin B. The signal transfer layer 607 isformed by providing the ultraviolet-curable resin A on the transferstamper 605 beforehand, and applying the ultraviolet-curable resin B forincreasing the adhesiveness to the first substrate 601 so as to causethe ultraviolet-curable resin A and the first substrate 601 to adhere toeach other. In this method, upon the application of theultraviolet-curable resin A over the transfer stamper 605, the signaltransfer has to be carried out by utilizing the viscosity of the resinsolely, without utilizing the weight of the transfer stamper 605.Therefore, an ultraviolet-curable resin having a low viscosity in arange of 30 mPa·s to 200 mPa·s desirably is used as theultraviolet-curable resin A.

Sample disks were produced, each of which was obtained by transferring apattern of recesses provided on the transfer stamper 605 as transfer-userecording tracks onto the ultraviolet-curable resin 604 so that a heightof projections of the transferred pattern was 0% to 50% smaller than adepth of the recesses of the transfer stamper 605. Disk noises of therecording tracks were measured, and the measurement results are shown inTable 1. The sample disks were produced using the ultraviolet-curableresins 604 having viscosities ranging from 10 mPa·s to 5000 mPa·s. Here,the weight of the transfer stamper 605 was set to be of 0.15 g/cm². Themeasurement was performed in the following manner. The informationsurface was reproduced by using a recording/reproduction head with alaser wavelength of approximately 400 nm and a numerical aperture (NA)of an objective lens of approximately 0.85, and rotating an optical diskat a linear velocity of 4.5 m/s. Levels of disk noise at 12 MHz(reproduction frequency band of signals with a frequency of 0.375 μm)were measured with a spectrum analyzer. Table 1 shows how much disknoise performances were improved as compared with disk noiseperformances in the case of recording tracks of the conventionalthick-substrate transfer-type optical disk. It should be noted that arate by which the depth/height of the transferred pattern decreased isreferred to as “Depth/Height Decrease” in Table 1.

TABLE 1 Depth/Height Decrease (%) 0 2.5 5 10 20 30 40 50 Improvement ofNoise 0 0.2 3 3.2 3.2 3.3 — — Performance (dB)

From the results shown in Table 1, it is seen that the disk noiseperformance was improved by setting the depth/height decrease to notless than 5%. In the case where the viscosity of the ultraviolet-curableresin 604 was set to be less than 30 mPa·s so that a depth/height of atransferred pattern was greater than that in the case where thedepth/height decrease was 5% (in the case where the depth/heightdecrease was less than 5%), the surface roughness of the transferstamper 605 was transferred in detail, thereby increasing the disknoise. In the case where a depth/height of a transferred pattern wassmaller than that in the case where the depth/height decrease was 30%(in the case where the depth/height decrease exceeds 30%), it wasdifficult to perform uniform transfer within the disk, thereby causingtransfer irregularities. These were confirmed. Furthermore, in the caseof a disk obtained using the ultraviolet curable resin 604 with aviscosity of higher than 4000 mPa·s so as to achieve a depth/heightdecrease of not less than 40%, it was impossible to perform themeasurement with respect to the disk due to transfer irregularities.Thus, it was confirmed that a noise amount was decreased as comparedwith the prior art by performing the transfer so that the depth/heightof recesses/projections of the transferred pattern was 5% to 30%smaller, preferably 5% to 20% smaller, than the depth/height ofrecesses/projections of the transfer stamper. Furthermore, it wasconfirmed that to adjust the depth/height decrease in a range of 5% to30%, the viscosity of the ultraviolet-curable resin may be set to be 30mPa·s to 4000 mPa·s.

Sample disks were produced by using transfer stampers 605 with trackpitches varying in a range of 0.2 μm to 1.0 μm, and disk noises of therecording tracks at a 12 MHz band were measured. Table 2 shows how muchthe disk noise performances with respect to recording tracks wereimproved as compared with the disk noise performance of the conventionalthick-substrate transfer-type optical disk. It should be noted that themeasurement was carried out in the same manner as that of themeasurement shown in Table 1. Here, the sample disks were produced usingthe ultraviolet-curable resin 604 having a viscosity of 50 mPa·s, andthe transfer stamper 605 having a weight of 0.15 g/cm².

TABLE 2 Track Pitch 0.2 0.25 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 (μm)Improvement of — 3.0 3.2 3.4 3.4 3.3 3.0 3.1 0 0 Noise Performance (dB)

According to the results shown in Table 2, the disk noise performancewas improved in the case where the track pitch was not more than 0.80μm. It was confirmed that in the case where the track pitch exceeded 0.8μm, the disk noise increased (the improvement of the noise performancewas decreased) since the surface roughness of the transfer stamper 605was transferred in detail. Besides, it was confirmed also that in thecase where the track pitch was decreased to less than 0.25 μm, it wasimpossible to perform uniform transfer within the disk, thereby causingtransfer irregularities. Thus, it was impossible to perform themeasurement in the case where the track pitch was 0.2 μm or less. Fromthe foregoing results, it was confirmed that the noise amount wasdecreased as compared with the prior art by setting the track pitch in arange of 0.25 μm to 0.8 μm.

The foregoing description refers to an example in which a phase-changerecording film is used as the thin film layer 103, but identical resultswere obtained also in the case where a reflection film made of Al, Ag,or an alloy of AgPdCu was formed and disk noise was measured.Furthermore, the foregoing describes the disk noises from grooves suchas recording tracks or space tracks, but the same results were obtainedin the case of disk noise from signal pits.

According to the present embodiment, an optical disk that exhibitsexcellent disk noise characteristics even in the case where arecording/reproduction head having an improved focusing performance witha reproduction wavelength of approximately 400 nm and an NA of anobjective lens of 0.85 is used as a reproducing means was obtained bysetting the pattern on the information surface of the transfer stamperso that the depth/height of recesses/projections of the pattern isgreater than the desired depth of recesses of the signal transfer layer,and by appropriately setting the viscosity of the ultraviolet-curableresin and the weight of the stamper in the formation and transfer of thesignal transfer layer by spinning.

EMBODIMENT 2

FIG. 9 is a cross-sectional view illustrating an optical disk accordingto an embodiment of an optical recording medium of the presentinvention. A 0.1 mm-thick disk made of polycarbonate is used for forminga first substrate 901. A signal transfer layer 902 is made of anultraviolet-curable resin, on one of whose surfaces signal pits orrecording tracks are formed as projections, which are formed bytransferring a pattern on a transfer stamper. The transfer stamper isformed in the same manner as that in Embodiment 1, and a 1.1 mm-thickdisk made of a resin is used for forming the transfer stamper to preventwarpage and improve rigidity of the transfer stamper, so as to allow fora plurality of transfer operations.

FIGS. 10A to 10E illustrate a process for forming the signal transferlayer 902 on the first substrate 901 as a base. First of all, a firstsubstrate 1001 as a base is fixed on a turntable 1002 by a diskcentering jig 1003 provided substantially at the center of the turntable1002 as well as by suction of a plurality of small vacuum holes (notshown) provided on an upper surface of the turntable 1002, so as toreduce the eccentricity of the first substrate 1001 from a rotationalaxis of the turntable 1002 (see FIG. 10A). An ultraviolet-curable resin1004 is applied with a dispenser on the first substrate 1001 fixed onthe turntable 1002 so that the ultraviolet-curable resin 1004 is spreadover a range of a predetermined radius substantially in a concentricform (see FIG. 10B). Furthermore, a transfer stamper 1005 is laminatedon the first substrate 1001 on which the ultraviolet-curable resin 1004is applied so that an information surface of the transfer stamper 1005faces the first substrate 1001.

The ultraviolet-curable resin 1004 is spread by spinning the turntable1002 in a state in which the first substrate 1001 and the transferstamper 1005 are laminated, while simultaneously a pattern ofrecesses/projections forming the recording tracks or signal pits on theinformation surface of the transfer stamper 1005 are transferred onto asurface of the ultraviolet-curable resin 1004 (see FIG. 10C). Here, theultraviolet-curable resin 1004 flows toward a periphery due to acentrifugal force generated by the spinning, which tends to make itdifficult to fill the ultraviolet-curable resin 1004 in a centralportion inside the range of the predetermined radius to which theultraviolet-curable resin 1004 is dripped. To compensate this, theultraviolet-curable resin 1004 between the first substrate 1001 and thetransfer stamper 1005 may be sucked toward the central portion by avacuum drawing mechanism 10A provided at the centering jig 1003.Furthermore, in order to transfer the pattern formed on the informationsurface of the transfer stamper 1005 to the ultraviolet-curable resin1004 with an approximately 90% of a depth/height therecesses/projections, a resin containing, for instance, an acrylic resinas a principal component, having a viscosity of approximately 150 mPa·s,is used as the ultraviolet-curable resin 1004, while a disk made ofpolycarbonate that is 120 mm in diameter and 1.1 mm in thickness, has acenter hole at center with a diameter of 30 mm, and is approximately 16g in weight (weight per unit area: 0.15 g/cm²) is used as the transferstamper 1005. It should be noted that, other than polycarbonate, apolyolefin-based resin or an acryl-based resin may be used for formingthe transfer stamper 1005.

The ultraviolet-curable resin 1004 formed between the first substrate1001 and the transfer stamper 1005 is cured when ultraviolet light isapplied thereto by an ultraviolet projector 1006 (see FIG. 10D), andthereafter, the transfer stamper 1005 is detached from theultraviolet-curable resin 1004 at an interface therebetween. Thus, onthe first substrate 1001 (corresponding to the first substrate 901 inFIG. 9), an ultraviolet-curable resin layer is formed on which thepattern of recesses/projections of the transfer stamper 1005 istransferred with a depth/height of approximately 90% of the depth/heightof the recesses/projections on the transfer stamper 1005: namely, asignal transfer layer 1007 (corresponding to the signal transfer layer902 in FIG. 9) is formed (see FIG. 10E).

As a means for detachment, for instance, a region 10B in which theultraviolet-curable resin is not filled may be secured in the centralportion in a disk obtained by combining the first substrate 1001 and thetransfer stamper 1005 with each other, and a mechanical detaching jigmay be inserted or compressed air may be injected between the firstsubstrate 1001 and the transfer stamper 1005. By so doing, they aredetached uniformly in a radial direction of the disk. A polyolefin-basedresin may be used as the material of the transfer stamper 1005 with thedetachability thereof taken into consideration, so as to ensure thedetachment at an interface between the ultraviolet-curable resin 1004and the transfer stamper 1005. Here, a surface roughness of space trackson the transfer stamper 1005 was determined to be 3 nm according to themeasurement by an atomic force microscope, whereas a surface roughnessof space tracks formed on the signal transfer layer 1007 correspondingto the foregoing transfer stamper 1005 was determined to be 1 nm. Afterthe signal transfer layer 1007 is formed, a phase-change recording filmof the same type as that in Embodiment 1 is formed on the signaltransfer layer 1007. It should be noted that in Embodiment 1, areflection film, a dielectric film, a recording film, and a dielectricfilm are laminated in the stated order, while in the present embodimentthey are laminated on the signal transfer layer 1007 in an inversedorder.

An adhesion layer 904 provided for adhering a thin film layer 903 and asecond substrate 905 as a thick substrate is formed by, for example,applying an ultraviolet-curable resin over at least one of the thin filmlayer 903 and the second substrate 905, and subjecting the same tospinning so that air bubbles contained in the ultraviolet-curable resinare removed and the thickness thereof is controlled. The secondsubstrate 905 is composed of an approximately 1.1 mm-thick disk made ofa resin such as polycarbonate. The thickness of the signal transferlayer 902 is controlled so that a focus position 906 where a laser lightemitted from the recording/reproduction head is focused falls on aposition determined according to a sum of the thicknesses of the firstsubstrate 901 as the thin substrate and the signal transfer layer 902.Thus, with the transparent layer 904 (by curing the ultraviolet-curableresin), the first substrate 901 with the signal transfer layer 902 andthe thin film layer 903 provided thereon and the second substrate 905are caused to adhere to each other.

With the present invention, it is possible to form an informationsurface having inverted recesses/projections as compared with thoseaccording to Embodiment 1 on the first substrate on the reproductionbeam incident side, and to provide a disk with excellent disk noiseperformance as in Embodiment 1 by appropriately setting the viscosity ofthe ultraviolet-curable resin and the weight of the transfer stamper inthe formation and transfer of the signal transfer layer by spinning.Furthermore, as to optical disks according to Embodiment 2, theimprovement of noise performances as compared with the conventionaloptical disk was obtained as a result, as is the case with the opticaldisk of Embodiment 1.

1. A method for producing an optical recording medium, comprising: afirst step of laminating a substrate and a transfer stamper with a notcured ultraviolet-curable resin interposed therebetween, the transferstamper having, on at least one of surfaces thereof,recesses/projections that provide information to be transferred; asecond step of transferring the information to be transferred of thetransfer stamper onto a surface of the ultraviolet-curable resin; athird step of detaching the transfer stamper from theultraviolet-curable resin at an interface therebetween after theultraviolet-curable resin is cured; and a fourth step of forming a thinfilm layer on the information-transferred surface of theultraviolet-curable resin, the thin film layer including at least one ofa recording film and a reflection film, wherein at least one of a weightof the transfer stamper and a viscosity of the ultraviolet-curable resinis set so that a surface roughness of the information-transferredsurface of the ultraviolet-curable resin is smaller than a surfaceroughness of the surface of the transfer stamper on which theinformation to be transferred is provided.
 2. The method for producingan optical recording medium according to claim 1, wherein in the secondstep, spinning is carried out in a state in which the substrate and thetransfer stamper are laminated, so that the ultraviolet-curable resin isspread and the information to be transferred of the transfer stamper istransferred to the ultraviolet-curable resin.
 3. The method forproducing an optical recording medium according to claim 1, wherein theultraviolet-curable resin has a viscosity of not less than 30 mPa·s andnot more than 4000 mPa·s.
 4. The method for producing an opticalrecording medium according to claim 3, wherein the ultraviolet-curableresin has a viscosity of not less than 30 mPa·s and not more than 500mPa·s.
 5. The method for producing an optical recording medium accordingto claim 1, wherein a depth/height of recesses/projections formed on theultraviolet-curable resin as a result of the transfer is 5% to 30%smaller than a depth/height of the recesses/projections of the transferstamper that provide information to be transferred.
 6. The method forproducing an optical recording medium according to claim 5, wherein thedepth/height of the recesses/projections formed on theultraviolet-curable resin as a result of the transfer is 5% to 20%smaller than the depth/height of the recesses/projections of thetransfer stamper that provide information to be transferred.
 7. Themethod for producing an optical recording medium according to claim 1,wherein a track pitch of recording tracks or signal pits to betransferred that are included in the information to be transferred ofthe transfer stamper is 0.25 μm to 0.8 μm.
 8. The method for producingan optical recording medium according to claim 7, wherein a width of therecording tracks to be transferred or a width of the signal pits is 30%to 70% of the track pitch.
 9. The method for producing an opticalrecording medium according to claim 1, wherein a depth of recordingtracks or signal pits to be transferred that are included in theinformation to be transferred of the transfer stamper is 10 nm to 100nm.
 10. The method for producing an optical recording medium accordingto claim 1, wherein the transfer stamper has a weight per unit area of0.03 g/cm² to 0.20 g/cm².
 11. The method for producing an opticalrecording medium according to claim 1, wherein the transfer stamper ismade of a resin material.
 12. The method for producing an opticalrecording medium according to claim 1, wherein the recording film ismade of a phase-change recording film material.
 13. The method forproducing an optical recording medium according to claim 1, wherein thethin film layer comprises a reflection film.
 14. The method forproducing an optical recording medium according to claim 1, wherein thestamper is positioned on an upper side with respect to the substrate.15. The method for producing an optical recording medium according toclaim 1, wherein the transfer stamper has a thickness of 0.3 mm to 1.1mm.
 16. An optical recording medium produced by the method for producingan optical recording medium according to claim 1.